Some vehicles have components that are ejected during flight. For example, various missiles, such as the tactical Tomahawk cruise missile, must eject an inlet cover following launch. The inlet cover is ordinarily coupled to the vehicle with a shear pin. When an adequate force is applied, the pin is sheared and the inlet cover is thrust away from the vehicle, with the coupling mechanism piston converting the excess pressure in the system to force to accelerate the cover away from the missile.
A careful balance between the force applied and the shear strength of the pin is required. If the shear strength of the pin is too small, the pin may prematurely shear, inadvertently decoupling the inlet cover from the vehicle. If the shear strength of the pin is too large, the force applied may not be adequate to decouple the inlet cover from the missile and the component may not be ejected when desired. The force applied may be increased, but at the risk of missile damage, increased hazard, or other ill effects.